Resistors are presently fabricated using a number of different methods, depending on the requirements of the circuit in which resistors are to be used. Resistor types such as thin film resistors, thick film resistors, wound wire resistors, molded axial leaded resistors, surface mount resistors and others are known in the art.
Thin film resistors are fabricated by first depositing a resistive material, then a conductor material, onto a substrate. A wide variety of substrate materials can be used, but these materials generally contain an oxygen compound to permit adhesion of the resistive film. Materials used for thin film resistors generally must also be capable of providing adhesion to a substrate. The resistor film forms as single points on the substrate in the vicinity of substrate faults or other irregularities that might have an excess of broken oxygen bonds. The points expand into islands that form continuous films.
This differs from typical thick film resistor fabrication for which the conductor is deposited first onto a substrate, followed by the resistive material. In general, thick film resistors are formed by adding metal oxide particles to glass particles and firing the mixture at a certain temperature and for a predetermined time period sufficient to melt the glass and sinter the oxide particles together. The resulting structure consists of a series of three-dimensional chains of metal oxide particles embedded in a glass matrix. The higher the metal oxide-to-glass ratio, the lower the resistivity.
The drawback of traditional thick and thin film resistor manufacturing is that both processes tend to have many process steps. Another drawback to these methods of manufacture is that they are generally not capable of providing resistor networks having multiple different or common values in a single device. Further, current methods of manufacturing resistors generally result in the leads being located at the periphery of the resistor device. Peripherally located leads often suffer from the problem that these leads can be easily bent, requiring, in certain circumstances, that the resistor be glued in place. The proposed methods are more versatile than existing methods in that a wide range of resistor devices can be built using a single sacrificial layer, and that the resistor devices can be designed without peripherally located leads.